remove LDA_C_PW from "old" pbe gradient correction

parser/parser-quantum-espresso/QuantumEspressoXC.py

@@ -900,6 +900,9 @@ CORRELATION_GRADIENT_CORRECTION = [
         'xc_terms': [{
             'XC_functional_name': "GGA_C_PBE",
         }],
+        'xc_terms_subtract': [{
+            'XC_functional_name': 'LDA_C_PW',
+        }],
         'xc_section_method': {
             'x_qe_xc_igcc_name':       "pbe",
             'x_qe_xc_igcc_comment':    "same as PBX, back-comp.",